1. Field of the Invention
The present invention relates to a process for preparing a composite, continuatuous-fiber-containing filament.
2. Description of the Background
The present invention relates to a flexible, composite, thermoplastic filament which contains endless (i.e., continuous) fibres and to the process for preparing it.
More particularly, the present invention relates to a flexible, composite, thermoplastic filament constituted by fibre bundles of endless fibres of any kinds, whether mineral, or organic or metal fibres, impregnated with a thermoplastic powder and coated with an external flexible, thermoplastic sheath, which may either be of the same type, or of a different type, as of the thermoplastic component of the powder.
In a large number of applications, heretofore dominated by the use of metal materials, composite materials were proposed which are constituted by a polymeric matrix and an inorganic reinforcer component, above all fibreglass or carbon fibres. Under conditions under which particularly high performance are required as regards the mechanical strength, long-fibre or, above all, endless-fibre composites are proposed.
The first type of long-fibre or endless-fibre composite, developed as an alternative to the metal materials, was characterized by having a matrix constituted by thermosetting polymers, typical example of which are epoxy resins, unsaturated polyester resins and bismaleimides. Fabrication technologies for processing these type of materials were, and still are, preimpregnation and pultrusion.
Both said technologies require that the fibres are caused to flow through suitable solutions of the thermosetting material, with consequent environmental problems and high process cost, owing to the need for managing the re-use and/or the storage of the used solvents.
In order to obviate this type of drawbacks, more recently composite materials were introduced which use thermoplastic polymers as their matrix. In this case, the relevant fabrication technology implies, when the composite is a long- or endless-fibre one, the preliminary fabrication of a semifinished intermediate.
An example of preparation of such a type of semifinished intermediate is reported in U.S. Pat. No. 3,742,106; in which the formation of a composite by impregnation of a continuous reinforcer filament in a thermoplastic molten mass is disclosed.
A further example of semifinished intermediate for composite with thermoplastic matrix is reported in Journal of Applied Polymer Science--Applied Polymer Symposium, vol. 47, p. 501, 1991, in which the preparation is described of an endless filament by spinning a mix constituted by reinforcer fibres and thermoplastic fibres.
U.S. Pat. No. 4,614,678 discloses the formation of a composite article by impregnating a fibre bundle with thermoplastic powders and coating said fibre bundle with an also thermoplastic sheath.